SELECTING THE FUEL SUPPLY LINES
6
0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8
1234510620
50 60 10080 200 400 800 1000600
3
6
9
12
15
22
30 45 61 76 95 122 152
V
PRESSURE DROP (mbar)
1234567810
20 30 40
PIPE DIAMETER
1,4
PIPE LENGTH (m)
1/2
3/4
1"
1" 1/2
6"
1" 1/4
4"
3"
2" 1/2
2"
=
G
as
output
N
mc
/h
f
1 - G20
= 0,62 - G25
1,18 - G31
{
f
V
15,34
Figure A
The following diagram enables pressure drop in a pre-existing gas line to be calculated and to select the
correct gas train.
The diagram can also be used to select a new gas line when fuel output and pipe length are known. The
pipe diameter is selected on the basis of the desired pressure drop. The diagram uses methane gas as
reference; if another gas is used, conversion coefficient and a simple formula (on the diagram) transform
the gas output to a methane equivalent (refer to figure A). Please note that the gas train dimensions must
take into account the back pressure of the combustion chamber during operations.
Control of the pressure drop in an existing gas line or selecting a new gas supply line.
The methane output equivalent is determined by the formula fig. A on the diagram and the conversion
coefficient.
Once the equivalent output has been determined on the delivery scale ( ), shown at the top of the
diagram, move vertically downwards until you cross the line that represents the pipe diameter; at this
point, move horizontally to the left until you meet the line that represents the pipe length.
Once this point is established you can verify, by moving vertically downwards, the pipe pressure drop
of on the botton scale below (mbar).
By subtracting this value from the pressure measured on the gas meter, the correct pressure value will
be found for the choice of gas train.
Example: - gas used G25
- gas output 9.51 mc/h
- pressure at the gas meter 20 mbar
- gas line length 15 m
- conversion coefficient 0.62 (see figure A)
- equivalent methane output = 9.51 = 15.34 mc/h
0.62
- once the value of 15.34 has been identified on the output scale ( ), moving vertically downwards you
cross the line that represents 1" 1/4 (the chosen diameter for the piping);
- from this point, move horizontally to the left until you meet the line that represents the length of 15 m
of the piping;
- move vertically downwards to determine a value of 1.4 mbar in the pressure drop botton scale;
- subtract the determined pressure drop from the meter pressure, the correct pressure level will be found
for the choice of gas train;
- correct pressure = ( 20-1.4 ) = 18.6 mbar
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V
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